Electrophysiological Insights into the Adaptability of Bletilla striata to Bicarbonate Stress in Karst Habitats

Bletilla striata, a perennial orchid of both medicinal and ecological value, exhibits remarkable adaptability to bicarbonate-rich karst environments. To elucidate its physiological and electrophysiological responses to bicarbonate stress, seedlings were cultivated for 45 days under NaHCO3 concentrations of 0, 5, 10, and 15 mM (n = 4), with the nutrient solution renewed daily. At 5 mM, biomass, chlorophyll content, electrophysiological traits, nutrient transport, metabolic indices, and conductance–resistance parameters did not differ significantly from controls, while intracellular water-use efficiency exhibited only a minor, non-significant increase—indicating stable physiological performance under low bicarbonate conditions. By contrast, higher concentrations (≥10 mM), particularly 15 mM, markedly reduced intracellular water-holding capacity (−35.90%), nutrient translocation capacity (−22.26%), and metabolic activity (−50.00%), alongside electrophysiological signatures of diminished capacitance (−48.69%) and elevated resistance (+147.61%), consistent with membrane injury and impaired ion transport. Although xylem pathways dominated HCO3− transport, the phloem—despite greater sensitivity—showed an increased relative contribution under stress, supporting partial compensatory allocation. Metabolically, severe stress induced a shift toward a “low-metabolism, high-efficiency” strategy, prioritizing water conservation over carbon assimilation. Collectively, Bletilla striata adopts a dual strategy: maintaining functional stability (and modest enhancement) under environmentally relevant bicarbonate concentrations, while shifting to conservative resource-use under excessive stress. These adaptive mechanisms highlight B. striata’s potential for ecological restoration and sustainable cultivation in bicarbonate-rich karst environments.